AES AND LEED STUDIES OF SURFACE STOICHIOMETRY OF PALLADIUM SILICIDE EPILAYERS ON SI(111)

The stability region of the (1 x 1) surface structure for ultrathin ep itaxial Pd2Si (0001) films grown on Si (111) under UHV conditions was studied by AES and LEED. It is shown that solid state epitaxy of a Pd2 Si layer (5-20nm thick) on Si causes Si-enrichment of the silicide, bo th its surface and the film. Monolayer Pd deposition on the silicide s urface at room temperature and recording of Si L2,3VV Auger line shape variation allows the stoichiometric Pd2Si formation to be determined. At Pd deposition being carried on the two-phase Pd2Si+Pd system is fo rmed. At the metal atom concentration being critical the silicide is f ormed which is more Pd-rich than Pd2Si. The stoichiometry thereof is y et not understood. This new compound is unstable and after being held in vacuum it transforms back into Pd2Si+Pd or Pd2Si depending on the r elative Pd or Si concentration. For all the phase transitions found th e only (1 x 1) surface structure having a different spot/background ra tio in the diffraction pattern is characteristic.